The present invention relates to a method for controlling ignition timing of an internal combustion engine which uses an electronic ignition timing control apparatus.
In a conventional electronic ignition timing control apparatus, the ignition timing when the engine is under load is set to an optimum value in accordance with the amount of intake air flow and the rotational speed of the engine, and the ignition timing during idling operation is set to a value which is retarded with respect to the timing under load, irrespective of the amount of intake air flow, in order to assure the stability of the engine. FIG. 1 shows a flow chart for an ignition timing control method in the conventional apparatus.
Referring to FIG. 1,
(i) Temperature of engine coolant is read in (step I).
(ii) Based on the temperature of the engine coolant, it is determined whether the engine is in a start condition or not (step II).
(iii) When the engine is in the start condition, an advance angle .theta. of the engine set to a predetermined start advance angle .theta.sta (step III).
(iv) When the engine is not in the start condition, it is determined whether an idle switch is on or not (step IV).
(v) When the idle switch is on, that is, when the engine is in idling operation, a base advance angle .theta..sub.1 which is a base for setting the advance angle is set to a predetermined idling advance angle .theta.idl (step V).
(vi) When the idle switch is off, that is, when the engine is under load the amount of intake air flow Q is first read in (step VI).
(vii) After step VI, the engine rotational speed (rpm) N is read in (step VII).
(viii) Based on a prestored data, the base advance angle .theta..sub.1 is determined from the amount of intake air flow Q and the engine rotational speed N (step VIII).
(ix) Based on a prestored data, a warm-up correction advance angle .theta..sub.2 is determined from the engine coolant temperature (step IX).
(x) The engine advance angle .theta. is calculated by adding the base advance angle to the warm-up correction advance angle .theta..sub.2 (step X).
(xi) Based on a prestored data, a lower limit .theta.min allowable to the advance angle .theta. is determined from the engine rotational speed N (step XI).
(xii) The advance angle .theta. is compared with the lower limit .theta.min, and if .theta.min.ltoreq..theta., the advance angle .theta. is outputted as the advance angle 1 (step XII).
(xiii) If .theta.min&gt;.theta., .theta.min is selected as the advance angle .theta. (step XIII).
In the above conventional ignition timing control method, at the transition from the loaded operation to the idling operation, the amount of intake air flow Q suddenly decreases and hence the advance angle .theta. is suddenly retarded. As a result, torque generated by the engine rapidly decreases, resulting in vibration and noise due to backlash of gears of a transmission, which causes degradation of drivability and uncomfortable feeling to a driver.